Method for preparing penicillin sulfoxides

ABSTRACT

6-Aminopenicillanic acid, 6-acylaminopenicillanic acids, 2alkanoyloxymethyl-2-methyl-6-acylaminopenam-3-carboxylic acids and the esters thereof are oxidized to the corresponding penicillin sulfoxides in inert solvents with ozone at a temperature between about -10* and 35* C. The penicillin sulfoxides obtained thereby are useful for conversion to cephalosporin antibiotics.

United States Patent Spry [451 Sept. 12,1972

[54] METHOD FOR PREPARING [56] References Cited PENICILLIN SULFOXIDESUNITED STATES PATENTS [72] Inventor: Douglas 0. Spry, Indianapolis,

Ind, 462 0 3,544,581 12/1970 Essery ..260/243 c [73] Assi nee: L1 dc IPrimary Examiner-Nicholas S. Rizzo g In d. 1 ompany Attomey-Everet F.Smith and Walter E. Buting [211 62,717 6-Aminopenicillanic acid,6-acylaminopenicillanic acids, 2-alkanoyloxymethyl-2-methyl-6- 521 US.Cl ..260/306.7, 260/239.1 and 51 Int. Cl. ..C07d 99/16 them arePenicillin [58] Field of Search ..260/239.1 306.7 sulfflides when atempera ture between about -10 and 35 C. The penicillin sulfoxidesobtained thereby are useful for conversion to cephalosporin antibiotics.

7 Claims, No Drawings METHOD FOR PREPARING PENICILLIN SULFOXIDESBACKGROUND OF THE INVENTION The chemical conversion of penicillinantibiotics to cephalosporin antibiotics has been known for some time.(R. B. Morin et al. J. Am. Chem. Soc, 85, 1896 (1-963), U.S. Pat. No.3,275,626.)

According to the art-recognized procedure, a 6- acylaminopenicillanicacid ester sulfoxide or a 2-acyloxymethyl-2-methyl-6-acylaminopenicillanic acid ester sulfoxide isheated under acid conditions to effect conversion to the cephalosporincompound.

The starting materials in the conversion reaction, penicillinsulfoxides, have been prepared with a variety of oxidizing agents. Forexample, the organic peracids such as p'eracetic acid, perbenzoic acidand mchloroperbenzoic acid and the inorganic oxidants, such as hydrogenperoxide and sodium periodate have'been employed with varying degrees ofsuccess.

It is an object of this invention to provide a novel method forpreparing penicillin sulfoxides which provides the desired penicillinsulfoxides in excellent yields substantially free of over-oxidationproducts.

SUMMARY This invention relates to a method for preparing 1 6 5/S 2 Lil.0

and penicillanic acid refers to the 2,2-dimethylpenam-3-carboxylic acidof the following formula:

s U 1 1 a 2 3 0 N COOH Likewise, the nomenclature used in thisdescription follows the cepham nomenclature according to which cephamrefers to the following structure According to the novel method of thisinvention, a penicillanic acid or ester thereof is reacted with ozone inan inert solvent at a temperature between about l0 and 35 C. to affordthe corresponding penicillanic acid or ester sulfoxide. The method isuseful for the preparation of a variety of penicillin sulfoxides. For

example, -aminopenicillanic acid, 6- acylamidopenicillanic acids,2-alkanoxyloxymethyl-2- methyl-6-acylamidopenam-3'carboxylic acids andthe esters thereof formed with non-oxidizable groups, such as thebenzyl, p-nitrobenzyl, benzhydryl, t-butyl and trichloroethyl esters,react with ozone to form the corresponding acid or ester sulfoxides.

The appropriate penicillanic acid or ester is dissolved or suspended inan inert solvent or solvent mixture, such as a mixture of water andacetone, and the solution is ozonized at a temperature between about l0and 35 C., preferably at -5 to 5 C. The ozone is generated by the actionof an electric discharge on a stream of oxygen according to presentlyknown methods. The penicillin sulfoxide is recovered from the reactionmixture byevaporation of the organic solvent, or lyophilization in thecase where water is employed as the inert solvent. The penicillinsulfoxides so prepared can be further purified by recrystallization orby absorption chromatography over a suitable adsorbent, such as. silicagel.

The novel method of the present invention affords penicillin sulfoxidesin high yields and in a substantially pure state free of over-oxidationproducts such as the sulfones.

The penicillin sulfoxides provided by this invention are useful for thepreparation of cephalosporin antibiotics by known procedures.

DETAILED DESCRIPTION The method of the present invention which comprisesthe facile oxidation with ozone of 6- aminopenicillanic acid,6-acylamindopenicillanic acids,2-alkanoyloxymethyl-2-methyl-6-acylamindopenam-3-carboxylic acids andthe esters thereof formed with non-oxidizable groups, can be representedby the following general equation:

wherein R is hydrogen, a unit negative charge or a nonoxidizable esterforming group, R is methyl or C -C alkanoyloxymethyl, R is Nl-l orprotected amino, phthalimido or an acylamido group represented by theformula wherein X is hydrogen, methyl or ethyl, Y is hydrogen, methyl,hydroxy, NR or protected amino, P-is phenyl, substituted phenyl or C -Calkyl, n is 0 or I, and when n is l, P is phenyl or substituted phenyland Y is hydrogen or methyl and when n is 0 and Y is hydrogen, hydroxy,NHJ' or protected amino, X is hydrogen with the limitation that when theR, substituent does not include an NH group, then R is hydrogen or anon-oxidizable ester forming group.

The term non-oxidizable ester forming group" refers to ester forminggroups which are commonly employed as carboxylic acid protecting groupsand which are unreactive with ozone under the conditions describedherein. lLlustrative of such groups are benzyl, benzhydryl,p-nitrobenzyl, 2,2,2-trichloroethyl, t-butyl, methyl and the like.

The term protected amino group refers to a substituted amino groupwherein the substituent group is one commonly employed for theprotection of the basic amino function such as those groups which formurethanes with the protected amino group. lllustrative of such groupsare benzyloxycarbonyl, pnitrobenzyloxycarbonyl,p-methoxybenzyloxycarbonyl, t-butyloxycarbonyl, t-amyloxycarbonyl,Z-(p-diphenyl)-isopropyloxycarbonyl, adamantyloxycarbonyl and the like.The term also has reference to other amino protecting groups such asacetyl, chloroacetyl, benzoyl and the like.

The term C -C alkyl refers to the straight or branched chain aliphatichydrocarbonradicals such as suitable coolant such as an ice-watermixture or an icemethyl, ethyl, n-propyl, isopropyl, n-butyl, iso-butyl,n-

amyl, sec-amyl and the like. Substituted phenyl refers to a mono, diortri-substituted phenyl ring represented by the formula Edam...

wherein R is C -C alkyl, C C alkoxy, halogen, hydroxy, nitro or Ni l orprotected amino and m is l or 2.

The term C -C alkyl" refers to methyl ethyl, npropyl, n-butyl, iso-butyland the like. C -C alkoxy refers to methoxy, ethoxy, n-propoxy,isopropoxy n-butyoxy, sec-butoxy and the like. Halogen refers to fluoro,chloro and bromo.

The term C -C alkanoyloxymethyl" refers to acetoxymethyl,propionyloxymethyl, n-butyryloxymethyl, isobutyryloxymethyl,n-valeryloxymethyl and the like.

. Examples of groups representative of R when in the above Formula 1, Ris an acylamido group, include acetamido, propionamido, butyrylamido,phenylacetamido, phenoxyacetamido, 2,6-dimethoxyphenylacetamido,a-methylphenoxyacetamido, aadimethylphenoxyacetamido, 4!-nitrophenylacetamido, 3,4-dichlorophenylacetamido,3-hydroxyphenylacetamido, 4-ethylphenylacetamido,4butyloxycarbamidophenylacetamido, oz-(benzyloxycarbamido)phenylacetamido, 4-methoxyphenylacetamido,a-hydroxyphenylacetamido, 4- chlorophenoxyacetamido,2-bromophenoxyacetamido, 4-isopropoxyphenylacetamido,a-ethyl-amethylphenoxyacetamido, 3,4-dimethylphenoxyacetamido,4-fluorophenylacetamido and like acylamido groups.

According to the present method the pencillanic acid or ester thereofrepresented by the Formula I is dissolved or suspended in an inertsolvent and ozone gas is allowed to pass through the solution orsuspension. The temperature of the reaction mixture is maintainedbetween about 1 and 35 C. and preferably between about 5 to C. Coolingto the desired temperature is accomplished by surrounding the reactionvessel with a salt mixture. Inert solvents are those which areunreactive with ozone and the starting material. Representative of theinert solvents which can be employed in the present invention are water,water in combination with low molecular weight ketones and alcohols suchas acetone, methanol and ethanol, the chlorinated hydrocarbons such asmethylene chloride, ethylene dichloride and chloroform, and esters suchas ethyl acetate and isopropyl acetate. A preferred inert solvent is al:l mixture of acetone-water. The inert solvent or inert solvent mixtureis desirably one in which the penicillanic acid or ester is at leastpartially soluble over the temperature range described above. Thoseskilled in the art will recognize that other inert solvents and mixturesthereof can be employed in the practice of the present method inpreparing particular penicillanic acid or ester sulfoxides.

The ozone gas is conveniently prepared in an ozone generator of the typecommonly employed in synthetic and analytical chemical work to produceozone by the action of an electric discharge-on oxygen. The ozone isgenerated in a stream of oxygen which is then passed directly into thereaction vessel. The percentage of ozone produced in the generator isvariable, depending on the rate of flow of oxygen as well as theintensity of the electric discharge selected. For convenience, thepercentage of ozone generated with any given flow setting for oxygen canbe determined iodometrically by titrating with sodium thiosulfate theamount of iodine liberated from a standard solution of potassium iodideby ozone from the generator. In this manner, the amount of ozone passingthrough the reaction mixture with time can be calculated. However, oneadvantage of the present method for preparing penicillinsulfoxides isthat ozone can be used in excess without producing over-oxidation.Therefore, the amount of ozone is not critical, provided that asufficient amount is supplied to the reaction mixture to providecomplete oxidation of the penicillin to the penicillin sulfoxide. Ingeneral, an excess amount of ozone is passed through the cooled reactionmixture to insure complete reaction. The time required for completeoxidation varies with the percentage of ozone generated in the oxygenstream.

The penicillin sulfoxide products are recovered from the reactionmixture and purified by evaporating the reaction solvent andcrystallizing the solid products obtained. One of the desirable featuresof the present process is that it provides substantially pure penicillinsulfoxides and thus obviates extensive purification procedures requiredwith other methods of oxidation wherein either incompletely oxidized orover-oxidized contaminants occur in the reaction product mixture.

Those skilled in the art will recognize that two isomeric penicillinsulfoxides are possible, as illustrated by the following formulae:

wherein R is hydrogen or an ester forming group.

idation with ozone of a compound of the. Formula I, 5

wherein R is acylamido or Nl-l affords-a mixture of the isomerico-acylamidopenicillanic acid sulfoxides or -aminopenicillanic acidsulfoxides. For example, 6- phenoxyacetamidopenicillanic acid affordsapproximately a 1:1 ratio of the aand B-sulfoxides.

When R, of Formula I is phthalimido, oxidation with ozone according tothe present method provides 6- phthalimidopenicillanic acid a-sulfoxideas the predominant product.

The amount of each isomeric penicillin sulfoxide present in the isolatedproduct can be determined from the nuclear magnetic resonance spectrumof the product.

In a preferred embodiment of the present invention,6-phenoxyacetamidopenicillanic acid (phenoxymethylpenicillin) isdissolved in water-acetone (1:1, vzv) and the solution is cooled to atemperature of about to 5 C. in an ice-salt mixture. A stream ofozone-containing oxygen is passed through the cold solution until anexcess of ozone has been passed into the reaction mixture. The reactionmixture is then evaporated to remove the acetone and the white solidprecipitate is filtered to yield 6-phenoxyacetamidopenicillanic acidBsulfoxide. The aqueous filtrate is lyophilized to yield v6-phenoxyacetamidopenicillanic acid a-sulfoxide.

In another embodiment of the present invention, a slurry of6-aminopenicillanic acid (6-APA) in water is maintained at a temperatureof about 5 C. while a stream of ozone-containing oxygen in excess ispassed through the cold suspension. A colorless clear solution results.The solution is lyophilized to yield a nearly quantitative yield of6-APA sulfoxide.

Previously known methods for the oxidation of 6-APA to 6-APA sulfoxideafford low yields of product. For example, the oxidation of 6-APA withsodium periodate is reported to yield only 8 percent of 6-APA sulfoxide.J. Org. Chem., 30, (12), 4388-9 (1965).

The following compounds are illustrative of the penicillanic acid andester sulfoxides which can be prepared by the practice of the presentinvention:

6-aminopenicillanic acid a-sulfoxide,

p-nitrobenzyl 6-aminopenicillanate oz-sulfoxide,

6-phthalimidopenicillanic acid a-sulfoxide p-nitrobenzyl6-phthalimidopenicillanate a-sulfoxide,

o-acetamidopenicillanic acid B-sulfoxide,

2,2,2-trichloroethyl 6-acetamidopenicillanate B-sulfoxide,

p.-nitrobenzyl fi-acetamidopenicillanate B-sulfoxide,

Z-B-acetoxymethyl-2-a-methyl-6-' phthalimidopenicillanic acida-sulfoxide, Z-B-propionoxymethyl-Z-a-methyl6- phthalimidopenicillanicacid a-sulfoxide, 6-(2',2-dimethyl-2'-phenoxyacetamido) lanic acid a andfi-sulfoxides, 2-B-acetoxymethyl-2-a-methyl-6-acetamidopenicillanic acid,B-sulfoxide, 2-B-butyryloxy-2-a-methyl-6-acetamidopenicillanic acidB-sulfoxide, 2,2,2-trichloroethyl Z-B-acetoxymethyl-Z-a-methyl-6-phenoxyacetamidopenicillanate a and 62 -sulfoxides, benzhydryl6-phenoxyacetamidopenicillanate a and ,B-sulfoxides,6-(2-hydroxy-2'-phenylacetamido)penicillanic acid a and B-sulfoxides,6-(2,6-dimethoxyphenylacetamido)penicillanic acid a and B-sulfoxides,6-(4-methylphenoxyacetamido)penicillanic acid a and ,B-sulfoxides,6-(3-chlorophenylacetamido)penicillanic acid a and B-sulfoxides,6-(2-hydroxy-2'-m-hydroxyphenylacetamido)penicillanic acid a and,B-sulfoxides, 6-'(2-amino-2-phenylacetamido)penicillanic acid a and,Bsulfoxides, -n-hexanoylaminopenicillanic acid B-sulfoxide,

6-(3,4-dichlorophenylacetamido)penicillanic acid a and B-sulfoxides andlike penicillanic acid sulfoxides.

The 6-acylamidopenicillanic acid sulfoxides provided by this inventionare useful for the preparation of antibiotics of the cephalosporin classaccording to the method described in US. Pat. No. 3,275,626.Accordingly, a 6-acylamidopenicillanic acid, for example6-phenoxyacetamidopenicillanic, is oxidized to the sulfoxide with ozoneaccording to the practice of this invention and esterified with asuitable ester forming compound, for example, 2,2,2-trichloroethanol.The ester is reacted under the conditions described in US. Pat. No.3,275,626 to provide a 3-methyl-7-acylamino- A -cephem-4-carboxylic acidester, for example, 2,2,2- trichloroethyl 3-methyll7-phenoxyacetamido-Acephem-4-carboxylate. Likewise, a2-alkanoyloxyrnethyl-Z-methyl-6-acylaminopenicillanic acid, inparticular a 2-alkanoyloxymethyl-2-methyl-6-phthalimidopenicillanicacid, for example, 2-acetoxymethyll2- methyl-6-phthalimidopenicillanicacid, is converted to the corresponding sulfoxide with ozone, thesulfoxide obtained thereby is esterified, and the sulfoxide ester isreacted under the conditions described in US. Pat. No.

penicil- 3,275,626, to provide a 3-alkanoyloxymethyl-7 kanoyloxymethyl-A-cephem-4-carboxylic acid ester respectively.

6-Aminopenicillanic acid sulfoxide, provided by the oxidation with ozoneas described herein, is likewise useful for the preparation ofantibiotics of the cephalosporin class. For example, 6-aminopenicillanicacid sulfoxide is acylated according to well known procedures to providea 6-acylaminopenicillanic acid sulfoxide which, on esterification,yeilds the corresponding 6-acylaminopenicillanic acid ester sulfoxide.The latter is then converted to a cephalosporin antibiotic compound aspreviously discussed.

The starting materials useful in the present process are known anddescribed by the prior art and can be prepared by known methods. Thus,for example, 6- phthalimidopenicillanic acid is prepared by the methodof Sheehan et al., J. Am. Chem. 800., 84, 2983 (1962).

The 6-acylamidopenicillanic acids are prepared by the EXAMPLE 1 Asuspension of 2.16 g. of 6-aminopenicillanic acid in 200 ml. of waterwas cooled in an ice bath and an oxygen stream containing ozone waspassed through the cold suspension for 3 hours. The ozone was generatedin a Wellsbach Ozonization apparatus at a rate of 3.4 g./hr Completesolution was obtained after about 2.5 hours of gas flow. The colorlesssolution was lyophilized to obtain 2.26 g. of 6-aminopenicillanic acidsulfoxide as a pale yellow solid.

Elemental analysis: Calculated: C, 41.38; H, 5.21; N, 12.07 Found: C,41.10; H, 5.34; N, 12.27 N. M. R. (D 1.32 (S, 3, a-methyl) InfraredAbsorption Spectrum: 1787 cm. (B-lactam) (mull) 1025, 1007 (sulfoxide)EXAMPLE 2 A solution of 3.5 g. of 6-phenoxyacetamidopenicillanic acid in50 m1. of acetone and 50 ml. of water was cooled in a salt-ice mixtureto a temperature of 0 C. and the solution was ozonized with stirring for2.5 hours. During this time a large excess of ozone was passed throughthe cold solution. The reaction solution was then evaporated in vacuo ata temperature of 45 C. to remove the acetone. The solid whiteprecipitate which formed during the removal of acetone was filtered andvacuum dried at 30 C. for 24 hours to yield 1.8 g. of6-phenoxyacetamidopenicillanic acid fi-sulfoxide. The aqueous filtratewas lyophilized to yield a pale yellow solid which, after drying at 30C. for 24 hours, gave 1.8 g. of 6-phenoxyacetamidopenicillanic acida-sulfoxide.

Elemental analysis:

B-sulfoxide Theory: C, 52.46; H, 4.95; N, 7.65 Found: C, 52.30; H, 5.02;N, 7.64 a-sulfoxide Theory: C, 52.46; H. 4.95; N, 7.65 Found: C, 52.25;H, 5.02; N, 7.48

Infrared absorption spectrum (CHCI cm. B-sulfoxide: 1020, 1035, 1065,1080 (sulfoxide) 1800 (fl-lactam) and 1690 (amide) a-sulfoxide: 1796,1730, 1700, 1080, 1065 and 1040. Nuclear Magnetic Resonance Spectrum: 6(DMSO D6) B-sulfoxide 1.22 (S, 3, a-methyl) 1.62 (S, 3, fi-methyl) 4.45(S, 1, H;) 4.65 (S, 2, CH,-O-phenyl) 5.95 (q .l=4,.1=l0, H. I 7.12(M-Aromatic) 8.27 (d .l=l0, 1, NH)

a-sulfoxide EXAMPLE 3 A solution of 186 mg. of 6-phtha1imidopenicillanicacid in 50 m1. of water and 5 ml. of acetone was cooled in an ice-saltmixture to a temperature of 0 C. The cold solution was then treated withan excess of ozone for about 1 hour. The acetone was removed from thereaction mixture by evaporation and the cloudy aqueous residue waslyophililized to obtain mg. of 6- phthalimidopenicillanic acida-sulfoxide as white crystals.

Elemental analysis:

Theory: C, 53.04; H, 3.90; N, 7.73 Found: C, 52.77; H, 4.13; N, 7.73Nuclear magnetic resonance spectrum: 5 (DMSO D6) 1.25 (S, 3,iii-methyl)- 1.68 (S, 3, fl-methyl) 7 (S, 4, Aromatic) EXAMPLE 4 Asolution. of one gram of 6-(2',2'-dimethy1-2'-phenoxyacetamidopenicillanic acid in 50 ml. of acetone and 50 ml. ofwater and the solution cooled to a temperature of 5 C. in an ice-saltmixture. The cold solution was ozonized for 1 hour and 15 minutes,during which time excess ozone was passed through the solution. Thereaction mixture was lyophilized to yield 1.04 g. of solid colorlessresidue. Based on the N. M. R. spectrum, the residue was a mixture ofthe B-sulfoxide and the a-sulfoxide in a ratio of 1.4/1. The infraredabsorption spectrum of the product run as a mull in mineral oil showedthe following principal absorption peaks: 1796, 1745, 1689, 1655, 1070,1038 and 1020 cm.

EXAMPLE When 6(2'-ethyl-2'-phenoxyacetamidopenicillanic acid wasozonized according to the procedure described by Example 4, there wasobtained a mixture of the ,8 and a-sulfoxides, as evidenced by the N. M.R. spectrum of the dried reaction product.

EXAMPLE 6 A-solution of 4 g. of 2,2,2-trichloroethyl2-,B-acetoxymethyI-Z-a-methyl-6-phenoxyacetamidopenicillanate in 80 ml.of acetone and 45 ml. of water was cooled to a temperature of l0 C. Thecold solution was ozonized with stirring until excess ozone had beenpassed through the solution. The reaction mixture was evaporated todryness in vacuo and the solid residue was chromatographed over a columnpacked with silica gel. The column was eluted by the gradient elutiontechnique with a benzene-ethyl acetate gradient. The eluant fractionswhich contained the same materials, as indicated by thin layerchromatography, were combined and evaporated to dryness to yield 430 mg.of 2,2,2-trichloroethyl 2-3-acetoxymethyl-2-a-methyl-6-phenoxyacetamidopenicillanate a-sulfoxide B-sulfoxide.

EXAMPLE 7 A solution of 0.16 g. of methyl 2B-acetoxymethyl-2a-methyl-6-acetamidopenicillanate in 25 ml. of acetone and 25 ml. ofwater was cooled in an icesalt mixture to a temperature of -3 C. andozonized for minutes at a rate of 1.18 mm. of 0 per minute. Thecolorless solution was evaporated in vacuo at a temperature of 50 C. toyield 0.169 g. of a white foam. The reaction product mixture waschromatographed over silica gel using an ethyl acetatebenzene mixture asthe gradient to yield 30 mg. of methyl Za-acetoxymethyl-Z a-methyl-6-acetamidopenicillanic acid ester B-sulfoxide and sulfoxide and39 mg. of the a-sulfoxide.

lclaim:

l. The method for preparing a penicillin sulfoxide of the formulawherein R is hydrogen, a unit negative charge or a nonoxidizable esterforming group, R is methyl or C -C alkanoyloxymethyl, R is Nl-lprotected amino, phthalimido or an acylamido group of the formulawherein X is hydrogen, methyl or ethyl, Y is hydrogen, methyl, hydroxy,Nl-l or protected amino, P is phenyl, substituted phenyl or C -C alkyl,n is 0 or 1, and when n is l, P is phenyl or substituted phenyl and Y ishydrogen or methyl and when n is O and Y is hydrogen,

h d ox ,NH *or rotected mino,X ish d o en,with tlie iimi tationthatiivhen the 1 substrtuterit dogs not include an Nl-l group, then R ishydrogen or a non-oxidizable ester forming group which comprises theoxidation with ozone in an inert solvent at a temperature between -l0and 35 C. of a penicillin compound of the formula s CH3 1 R2 O= C 0 ORmethod of claim 3 wherein the starting compound is6-phenoxyacetamidopenicil-

2. The method of claim 1 wherein the starting penicillin compound is6-aminopenicillanic acid and the inert solvent is water.
 3. The methodof claim 1 wherein R1 is an acylamido group.
 4. The method of claim 3wherein the starting penicillin compound is6-phenoxyacetamidopenicillanic acid.
 5. The method of claim 3 whereinthe starting penicillin compound is p-nitrobenzyl6-phenoxyacetamidopenicillanate.
 6. The method of claim 3 wherein thestarting penicillin compound is 2,2,2-trichloroethyl6-phenoxyacetamidopenicillanate.
 7. The method of claim 3 wherein thestarting penicillin compound is 6-acetamidopenicillanic acid.